/*it is from linux list */  
#ifndef LIST_H  
#define LIST_H 
  
struct list_head {  
    struct list_head *next, *prev;  
};  
  
typedef struct list_head list_t;  
  
#define LIST_HEAD_INIT(name) { &(name), &(name) }  
  
#define LIST_HEAD(name) \
    struct list_head name = LIST_HEAD_INIT(name)  
  
#define INIT_LIST_HEAD(ptr) do { \
    (ptr)->next = (ptr); (ptr)->prev = (ptr); \
} while (0)  
  
/** 
 * list_add - add a new entry 
 * @new: new entry to be added 
 * @head: list head to add it after 
 * 
 * Insert a new entry after the specified head. 
 * This is good for implementing stacks. 
 */  
void list_add(struct list_head *new, struct list_head *head);  
  
/** 
 * list_add_tail - add a new entry 
 * @new: new entry to be added 
 * @head: list head to add it before 
 * 
 * Insert a new entry before the specified head. 
 * This is useful for implementing queues. 
 */  
void list_add_tail(struct list_head *new, struct list_head *head);  
  
  
/** 
 * list_del - deletes entry from list. 
 * @entry: the element to delete from the list. 
 * Note: list_empty on entry does not return true after this, the entry is in an undefined state. 
 */  
void list_del(struct list_head *entry);  
  
/** 
 * list_del_init - deletes entry from list and reinitialize it. 
 * @entry: the element to delete from the list. 
 */  
void list_del_init(struct list_head *entry);  
  
  
/** 
 * list_move - delete from one list and add as another's head 
 * @list: the entry to move 
 * @head: the head that will precede our entry 
 */  
void list_move(struct list_head *list, struct list_head *head);  
  
  
/** 
 * list_move_tail - delete from one list and add as another's tail 
 * @list: the entry to move 
 * @head: the head that will follow our entry 
 */  
void list_move_tail(struct list_head *list,  
                  struct list_head *head);  
  
/** 
 * list_splice - join two lists 
 * @list: the new list to add. 
 * @head: the place to add it in the first list. 
 */  
void list_splice(struct list_head *list, struct list_head *head);  
  
/** 
 * list_empty - tests whether a list is empty 
 * @head: the list to test. 
 */  
static int list_empty(struct list_head *head)  
{  
    return head->next == head;  
}  
  
/** 
 * list_dequeue - dequeue the head of the list if there are more than one entry 
 * @list: the list to dequeue 
 */  
struct list_head * list_dequeue( struct list_head *list );  
  
/** 
 * list_entry - get the struct for this entry 
 * @ptr:    the &struct list_head pointer. 
 * @type:   the type of the struct this is embedded in. 
 * @member: the name of the list_struct within the struct. 
 */  
#define list_entry(ptr, type, member) \
    ((type *)((char *)(ptr)-(unsigned long)(&((type *)0)->member)))  
  
/** 
 * list_for_each    -   iterate over a list 
 * @pos:    the &struct list_head to use as a loop counter. 
 * @head:   the head for your list. 
 */  
#define list_for_each(pos, head) \
    for (pos = (head)->next; pos != (head); \
            pos = pos->next)  
              
/** 
 * list_for_each_safe   -   iterate over a list safe against removal of list entry 
 * @pos:    the &struct list_head to use as a loop counter. 
 * @n:      another &struct list_head to use as temporary storage 
 * @head:   the head for your list. 
 */  
#define list_for_each_safe(pos, n, head) \
    for (pos = (head)->next, n = pos->next; pos != (head); \
        pos = n, n = pos->next)  
  
/** 
 * list_for_each_prev   -   iterate over a list in reverse order 
 * @pos:    the &struct list_head to use as a loop counter. 
 * @head:   the head for your list. 
 */  
#define list_for_each_prev(pos, head) \
    for (pos = (head)->prev; pos != (head); \
            pos = pos->prev)  
              
/** 
 * list_for_each_entry  -   iterate over list of given type 
 * @pos:    the type * to use as a loop counter. 
 * @head:   the head for your list. 
 * @member: the name of the list_struct within the struct. 
 */  
#define list_for_each_entry(pos, head, member)              \
    for (pos = list_entry((head)->next, typeof(*pos), member);   \
         &pos->member != (head);     \
         pos = list_entry(pos->member.next, typeof(*pos), member))  
  
#endif  